1. Field of the Invention
This invention relates in general to gas compressors and pumps, and, particularly, to the extraction of energy from a tuned oscillating mass, and more particularly relates to a tuned resonant oscillating mass pump structure and assembly which can be conveniently and readily mounted either inside automotive tires or outside on their rims for maintaining optimum tire pressure and generating electricity from the movement of the tuned oscillating mass in the pump.
2. Description of the Related Art
The Society of Automotive Engineers estimates that a vehicle whose tires are inflated at 20% below their specified pressure is penalized 3-5% in terms of fuel economy.
The Department of Energy estimates that this country wastes 4.2 million gallons of gasoline per day due to increased rolling resistance caused by low tire pressures. Firestone Corporation studies show that the serviceable life of a metric radial tire designed for 35 psi, but inflated to only 24 psi, is reduced by 50%. The National Highway Transportation and Safety Administration suggests that low tire pressure may cause 250,000 accidents annually. Finally, improperly inflated tires can degrade the performance of the most well-designed and finely tuned suspension system, and even adversely affect anti-lock braking.
Nevertheless, the inconvenience of checking tire pressures deters many from this simple maintenance routine; the result, according to Highway Administration figures, is that about half the passenger cars on the road have at least one under inflated tire. Because ride and handling degrade so gradually, a slow leak may not be detected until it becomes dangerous or a tire is ruined. Even sound tires are permeable and can lose as much as 25% of their air pressure over a year's time.
Existing tire pressure management systems, either integrated to a monitoring system or by themselves, are known in the art. One such class of systems have generally comprised a pump mounted on the vehicle wheel to rotate therewith, the plunger of the pump being positively actuated by engagement with an element, usually a cam, mounted on the axle or an axle support.
A pump apparatus that can be attached to the valve of an automobile tire in order to pressurize the pneumatic chamber of the tire and thereby maintain tire pressure at a preset value is described in U.S. Pat. No. 5,201,968, "Tire Pressuring and Regulating Apparatus", inventor Grant J. Renier. The apparatus utilizes cyclic forces generated at a location eccentric from the axis of rotation of a rolling wheel. The apparatus comprises pumps responsive to the cyclically ever changing resultant force of centrifugal and gravitational forces for pressurizing air to inflate the pneumatic tire.
Many of these systems usually require mechanical modification of the axle or its supporting structure to accommodate the cam element.
Another class of these conventional systems uses a centrifugal-force pump concept for placement inside automotive tires for the purpose of maintaining optimum tire pressure.
Another class of self-energizing tire pressure management systems utilizes gravity to drive one or more reciprocating pumping plungers. An example is found in U.S. Pat. No. 2,055,983 to Peo for an automatic tire inflation system which is detachably mounted on the wheel with little to no mechanical modification of the wheel or axle structure, and has one or more pumping plungers operated by a weight which reciprocates in the pump frame solely in response to gravity as the wheel rotates.
Yet another class places a compressor unit on a vehicle chassis and pumps air to the tires through the wheel bearings while the vehicle is moving. This system adds a great deal of weight to the vehicle as well as compressor noise during its operation.
However, these conventional systems are inefficient and cumbersome in actual installation and use. Therefore, there is a need for gas compressors and pumps which can extract useful energy and more particularly, a need for a pump structure and assembly which can be conveniently and readily mounted either inside automotive tires or outside on their rims for maintaining optimum tire pressure and generating electrical power.
In a totally different application relating to crankshafts, a device commonly used to damp crankshaft vibrations uses a resonant tuned oscillating mass to generate mechanical energy and power. Such devices are described in textbooks such as Mechanical Vibrations by den Hartog and The Standard Handbook for Mechanical Engineers by Baumeister & Marks. The device uses an oscillating mass whose frequency of oscillation is intrinsically tuned to the vibrational frequency of the crankshaft to which it is attached. This matching of pendulum frequency to vibrational speed occurs, as will be shown, at all vibrational speeds.
FIG. 1 is a schematic of a pendulum/pivot as it oscillates under the influence of both a cyclic gravity force, F.sub.g, and a radial centripetal acceleration, F.sub.c.
As can be seen, the centripetal acceleration force F.sub.c can be resolved into two components, one along the axis of the pendulum, F.sub.a, and one perpendicular to the pendulum, F.sub.t. This perpendicular force will tend to restore the pendulum to its centered condition. Because of this, the pendulum will oscillate back and forth in the radial centripetal acceleration field.
If the polar moment of inertia of the pendulum mass about its center of gravity is neglected, for the sake of convenience in illustration, the motion of the pendulum is simply described by the following differential equations showing the summation of torques about the pendulum pivot axis.
The torque about the pendulum pivot axis is given by computing the radial acceleration force on the pendulum mass M.omega..sup.2 L.sub.3, and multiply it by the sine of the difference between angles .theta..sub.1 and .theta..sub.2, and by the lever arm, L.sub.2, where, L.sub.1 is the distance between the pivot point 16 and the center of rotation of the device to which it is attached, L.sub.2 is the length of the pendulum (lever arm) and L.sub.3 =L.sub.1 +L.sub.2 : EQU .tau.=M.omega..sup.2 L.sub.3 sin (.theta..sub.1 -.theta..sub.2)L.sub.2( 1)
The moment of inertia that the pendulum mass makes about its pivot point is : EQU I.sub.p =ML.sub.2.sup.2 ( 2)
By geometry: EQU L.sub.2 sin (.theta..sub.2)=L.sub.3 sin (.theta..sub.1) (3)
For the case of relatively small angles, ##EQU1## which results in the simplifying approximations: ##EQU2##
The effective angular spring constant created by the centripetal acceleration field on the pendulum mass may be thus expressed as: ##EQU3## Now, the natural frequency of a mechanical oscillator consisting of a moment of inertia, I.sub.p, restrained by a torsional spring, K.sub.q, is well known to be: ##EQU4## Substituting the relations of (2) and (8) above, yields a natural frequency for the pendulum of: ##EQU5## It is seen from the above equation that the natural frequency, .omega..sub.n, of the pendulum will be exactly equal to the vibrational velocity, w, of the device to which it is attached if L.sub.1 =L.sub.2. The pendulum's natural frequency thus tracks the vibrational speed of the crankshaft for all vibrational speeds.
As mentioned earlier, the phenomenon discussed above is well known in the area of harmonic dampers for crankshafts. Sources which describe it include den Hartog and Marks. The natural frequency of such a damper is tuned to a harmonic of the crankshaft's rotational speed, with the harmonic corresponding to the number of independently firing pistons on the crankshaft. This permits it to resonantly absorb transient forces from the pistons at all crankshaft speeds. This is the most efficient point to transfer vibrational energy to a resonator. The resonator (harmonic damper) increases its amplitude of oscillation until dissipating frictional forces are sufficient to suppress crankshaft vibration. In the crankshaft application, the motion of the pendulum is used to generate frictional energy dissipation. This frictional energy dissipation reduces the amplitude of vibration of the crankshaft but produces no useful work. Vibration damping is the primary objective in the crankshaft application.
The two totally different applications discussed above provide the background for the present invention which fulfills a need for gas compressors and pumps which can extract useful energy and more particularly, a need for a pump structure and assembly which can be conveniently and readily mounted either inside automotive tires or outside on their rims for maintaining optimum tire pressure and generating electrical power.